The Rookery is a transitional building, employing both masonry bearing walls in its street facades and cast-iron columns, wrought-iron spandrel beams, and steel beams elsewhere in its structure. The interior light court lobby was remodeled by Frank Lloyd Wright in 1905. / 'The Rookery was one of the first buildings in the nation to make use of a large light court in its center, which filled offices with natural light and enabled the creation of a glass-enclosed courtyard. The building was also known for its ornament, inculding the grid-work of the atrium ceiling and ethereal designs in wrought iron and marble. The elevators have open cages and the lobby is topped with a cast iron skylight. A winding staircase spirals up through the interior courtyard.' Source: http://members.aol.com/dahlia773/rook.htm